Finite‐Element Modeling and X‐Ray Measurement of Strain in Passivated Al Lines during Thermal Cycling

Abstract

Narrow‐pitch encapsulated Al lines are used as interconnect metallization in integrated circuits. We have measured the principal strain state of Al alloy lines passivated with silicon nitride directly as a function of temperature. We compare these results with calculations of the strain state in these lines using finite‐element modeling. The measured strain‐temperature behavior shows good fundamental agreement with finite‐element modeling, although the magnitude of the strains measured with x‐rays is less than that predicted by modeling due to voiding in the lines.

Measurement and interpretation of strain relaxation in passivated Al–0.5% Cu lines

“…The strain relaxation experiments were performed using grazing incidence x-ray scattering (GIXS) at the Stanford Synchrotron Radiation Laboratory (SSRL) under operating conditions described previously. 6,9 No attempts were made to measure the strain gradients through the thickness of the passivated lines. The ͑42 2͒ reflection was scanned in the "length (X)" and "width (Y)" orientations of the lines, and the (222) reflection was measured in the "height (Z)" orientation.…”

“…[1][2][3][4][5][6][7][8] Usually the interplanar spacing of a particular reflection is measured at several inclination angles (c) relative to the surface normal. The interplanar spacing is then fit to a linear function of sin 2 c. From measurements of a uniform film, and lines parallel to and perpendicular to the diffraction plane, the principal strains in the line can be obtained.…”

“…An alternate method was developed by Besser et al, 6,9 who used x-rays from a synchrotron source in the grazing incidence geometry. In their method, the principal strains along the length, width, and height of the line were measured directly.…”

An investigation of the impact of a Ti barrier metal on the thermal stress field in passivated aluminium lines and vias in VLSI systems using finite element modelling approach

“…Although attention has mainly been focused on failure in straight lines with a small cross-sectional area, it has recently been realized that the vias (or studs) which connect lines in di erent metallization layers tend to su er a much higher failure rate than the Al lines themselves. Thus, the use of the ® nite element modelling (FEM) technique (Jones and Basehore 1987, Greenebaum et al 1991, Cifuentes and Shareef 1992, Sauter and Nix 1992, Besser et al 1993, Shi and Tu 1994, Shen 1997 in assessing residual thermal stress patterns in multilevel metal structures has become more and more important. Using the FEM approach it is possible to identify`weak' parts of the structure (the highest stress regions) and to optimize the structure with respect to the residual stress, as well as the processing parameters (temperatures, layer thickness).…”

“…Recently FEM techniques (Cifuentes andSharref 1992, Igic andMawby 1998 a,b) have been proposed which overcome all previously noted weaknesses of the so called`frozen view' FEM approach (Jones and Basehore 1987, Greenebaum et al 1991, Sauter and Nix 1992, Besser et al 1993. The`frozen view' technique assumes that at some high temperature (determined by the processing) the structure is in a stress-free state, and that the stresses are generated as the temperature is reduced to room temperature.…”